Oscillator from a differential output amp

This CR4 is not normally responding to homework situation. BUT, you did your homework and the question is a bit interesting.

There is no question, that a simple single sided (not differential, as the question) amplifier a positive feedback will ensure oscillation, sometimes even when it is not wanted.

In your case, you have a differential amplifier with an excellent CMMR Common Mode Suppression. If you drive is in a single ended mode, CMMR comes fully into play. So, if you have a 40dB feedback and a 80dB CMMR working against it, how much oscillation do you get? Just stick to other TLxxx members of the simple single ended family, and you will be fine.

Normally its a case of designing an amplifier and getting an oscillator... Or design an oscillator and getting nothing!!

I don't know what frequency you are hoping to get out of the TL592 but its voltage gain is pathetic!

Have you tied the gain set pins to anything? Shorting them or tying them to supply or ground will stop the thing from working as an amplifier...

As post #1 says just use a simple 741 op amp, why bother with a video amplifier? if you want the high frequency there are plenty of alternative op amps and most will quite happpily sing to you when wired up!!

John.

I would use the simple single ended output op-amp to start - 741 was a good suggestion. Have you looked up op-amp oscillator circuits on the internet. It is a misconception that positive feed necessarily makes an oscillator. Positive feedback in an op-amp generally results in maximum gain.

Er, NO!

Op-amp basics:

negative feedback = reduced, stable amplification

no feedback = max. stable amp. according data sheet

tiny positive feedback = more, unstable amp.

positive feedback = oscillation

Read and learn from the manufacturers Application Notes, or just go back to school.

Try It!

Connect the output of a 741 to the +V input and tie the negative input to any potential. The output will go to the rail and stay there. It will not oscillate.

Positive feedback is used all the time to generate rail to rail output comparator configurations with hysteresis. They are not oscillators but very useful for undervoltage and overvoltage detectors in a variety of circuits.

Before you get all high on yourself and suggest people go back to school you should get your facts straight.

I am not going to get involved in this disagreement as a small amount of feedforward positive signal can certainly increase the gain of an op amp.

A lot of positive feedback will NOT necessarily cause oscillation just latch up to either rail of the output.

John

Yes! DC positive feedback will most likely produces latching.

though I plan to tune it down to LFO land...

What the heck is LFO land?? Does it have a meaning in Hz?? If what you need is just an audio oscillator, I would just go with a conventional op amp with which there are many oscillator circuits.

Could we get a few more details please?

Bill

I Thank you all for suggestions... (this is a hobby project, not homework)...

I was trying to use amp because I have an excess of them and a limited stock of single ended amps. I was trying to adapt (at the bench) a Wein-bridge styled circuit for this...

"Deadlines" and your suggestions have lead me to purchase some more op-amps for myself.

I am aiming for a frequency anywhere around 0.05-1 hz to regulate LED driver for a model.. I don't need anything really accurate or stable or long lived. (infact drift will be nice) .. just something quick and dirty...

again thank you.

Regards all !

<< ... I've tried positive feedback on both +/- sides of in/out. .. >>

I liked to add the point which has been covered briefly by:

leveles #4

<<.... negative feedback = reduced, stable amplification >>

Feed-back on Inverter I/P (-) terminal is NOT POSITIVE-FEED-BACK

Regards.